Color photographic silver halide materials are used to provide color images with the use of certain dye forming compounds that are usually in the various photosensitive silver halide layers of the materials. These dye forming compounds are conventionally known as "dye forming couplers" and are reactive with suitable oxidized forms of color developing agents used during photoprocessing to provide the desired dye images. Since most of such silver halide materials (such as color negative films and color papers) provide images based on what is known in the art as "subtractive color mixing", they typically include dye forming couplers that will provide cyan, yellow and magenta dyes in the appropriate photosensitive layers.
Pyrazolotriazoles have been known to be useful photographic magenta dye forming couplers for some time, and various processes are known for preparing them, all of which usually include various chemical reactions taken in specific order. Such processes add functionality that defines the desired dye forming coupler early in the synthesis. These processes result in the lack of generality of the process and the need to make different intermediates for different dye forming coupler end products.
It is well known in the art [for example, U.S. Pat. No.5,183,728 (Romanet et al), U.S. Pat. No, 5,457,210 (Kim et al) and U.S. Pat. No. 5,565,572 (Potenza et al)] that coupler precursors defined by Formula I below can be converted to coupler intermediates defined by Formula II (wherein R.sub.3 is an alkyl group and R.sub.4 is hydrogen) by reacting a Formula I compound with a primary aliphatic amine in refluxing tetrahydrofuran (THF). ##STR1##
This reaction works well if R.sub.3 is an alkyl group and R.sub.4 is hydrogen, but it does not work well (i.e. resulting in long reaction times and/or low chemical yields) if either R.sub.3 or R.sub.4 is an aromatic group.
It is also known from the noted Kim et al and Potenza et al patents that this same transformation can be affected by adding triethylamine to the reaction mixture. ##STR2##
While this reaction works well if R.sub.3 is an alkyl group and R.sub.4 is hydrogen, if either R.sub.3 or R.sub.4 is an aromatic group, the results (i.e. chemical yield, reaction times, and product purity) are variable and substrate dependent. Additionally, disposal of reaction process waste material containing an organic base like triethylamine presents a more serious environmental problem.
There remains a need in the photographic industry for a synthetic method for preparing dye forming coupler intermediates of the pyrazolotriazole type that can be carried out with reactants containing aromatic groups with high yield, high purity and shortened reaction time, while the environmental impact of waste disposal is minimized.